Electricity is an essential part of modern life. Electric-power transmission is the bulk transfer of electrical energy, from generating power plants to electrical substations located near demand centres. Transmission lines mostly use high-voltage three-phase alternating current (AC). Electricity is transmitted at high voltages (110 kV or above) to reduce the energy lost in long-distance transmission. Power is usually transmitted through overhead power lines. Underground power transmission has a significantly higher cost and greater operational limitations but is sometimes used in urban areas or sensitive locations. Most recently, submarine power cables provide the possibility to supply power to small islands or offshore production platforms without their own electricity production. On the other hand, submarine power cables also provide the possibility to bring ashore electricity that was produced offshore (wind, wave, sea currents . . . ) to the mainland.
These power cables are normally steel wire armoured cables. A typical construction of steel wire armoured cable 10 is shown in FIG. 1. Conductor 12 is normally made of plain stranded copper. Insulation 14, such as made of cross-linked polyethylene (XLPE), has good water resistance and excellent insulating properties. Insulation 14 in cables ensures that conductors and other metal substances do not come into contact with each other. Bedding 16, such as made of polyvinyl chloride (PVC), is used to provide a protective boundary between inner and outer layers of the cable. Armour 18, such as made of steel wires, provides mechanical protection, especially provide protection against external impact. In addition, armouring wires 18 can relieve the tension during installation, and thus prevent copper conductors from elongating. Possible sheath 19, such as made of black PVC, holds all components of the cable together and provides additional protection from external stresses.
Patent application CN101950619A discloses an armouring structure for a high voltage submarine cable. The armouring structure is a mixed armouring layer in an annular form and is made from round copper wires and non-magnetic stainless steel wires. The round copper wires and non-magnetic stainless steel wires are arranged in alternation. However, due to the application of two materials, the production process becomes complex. Moreover, the use of copper makes this armouring structure quite expensive.
Alternatively, it is possible to merely use steel wires to construct armouring structure of power cables. Since the application environment of these cables contains moisture, certain corrosion protection for these cables is desired and stainless steels are applied as armouring wires. However, when the application environment is very corrosive, especially for submarine cables because the cable (core) heats up and that the corrosion resistance in sea water of the traditional stainless steel alloys strongly degrades with raising temperature, the corrosion protection of the power cables becomes crucial. Therefore, stainless steel wires with galvanized layer as corrosion resistant layer are considered to be used as armouring wires in particular for submarine power cables.
However, through a conventional galvanizing process, the coated galvanized layer is usually not firmly adherent to the stainless steel wire. Thus, the galvanized layer is easily laminated and peels off from the armouring steel wire under external forces. Therefore, a failure of corrosion protection occurs and limits the life of the power cable.